Trunking system



April 24, 1928.

1,666,988 w. 5. BLAUVELT TRUNKING SYSTEM Filed April 27, 1927 2 Sheets-Sheet 1 by W/bmey April 24, 1928. 1,666,988

W. G. BLAUVELT TRUNKING SYSTEM Filed April 27. 1927 2 Sheets-Sheet 2 jf/ome y of Fig. 1, show:- portion's 'offgt "group of '(SD Q' selectors having; accessi to 46 trunks.

Patented Apr. 24, 192

p I 1,656,988? 1 F G; um-m2 Y ki mi Anthem rmmm isrfif'rEL'E'ertAriIooMPeNY; ATCORPORAYTIONOYF NEW'YORK.

' TRUNKING sffsirlrjfl This invention relatesto telephone. ex change system'sand} more 'p':trt1cularly to tru'nlr'i'ngi arrangementstherefor;- and has for its". object to, increaseth'e eifioieney with which trunks and switching'means may" be cmplhyefcl witlrou t impairing the service rendered.

It:.is"n'ot possible in? a large machine switching system to give all selector switches I of one switchingstage access to all of the? trunksextending to the nexteswlitching stage. Twoiigeneral methodshe-ve heretofore been: devised toidistrihi'ite thetrunks'of a trunk gro'up before selector .switches ,in such avway" as-t'o eq uahze thetra'ffic over all of the trunks and. to provide;- as nearly as: possible that theremay be idle trunks'availhble a t-all time for the use: of the selectors. 'A'ccording ftot the first" 0% these metliods; -knownas the graded multiple, the: selectors anfcl the trunks ofeach switching stage arewdividedF intor' groups; A difi'erent groupi ottrunks serves as 'firstv-choicefor each: group? of: selectors.;, Other additi'omil'zgroupsof trunks'ser'Ve as;

se'contliechoice: for: a: plurality of groups of ual to each other; but each-group: 'ofiitr'unks is larger than the number-toiwhicheachsee lector hesacceSsz' The trunksmre thehmill? v ti pled TaCC OPd'ingi, to 21711" arbitrary random are I rarigement before the selectors Ot-thrsgroup;

so that each: selector Will have accessto only a portionof the total number oftruiiksi The present invent-lends: an? improvement: on t-he above methods ingfiha't it'emplbys a" graded multiple, the trunks 025. each groupbeing interchanged WljlZll-Lfl: their respect ve groups sothet the groups of lines lizwlng ac? cess thereto overlap each; other and-theorder: of'sele'ction of the trunks a -ndzthe rover-lap;

ping of thegroups oflinesgiveirise to least 2111- zvpproximately random"arrangement:

One: specific emhodiment of the invention" is set forth in the drawings. Figures-'l' 'ari'd" 2; when arranged with" Fig; 2 at 'the right The requirements for: a per f ctly there would stil l 'beiohly tell-trunks,- which 1 r We at f figures which arei=morepreetice1= v r a d m aiii ah'gement ofatrunksis'thztt if 'a-ny p'arti 'cuf ular number of them: wreknwwv -to bexbu y;

the probability of one set oft-runksof that" most common-ly employed; the'- e;rrarrge-i ments or permutations would numter ove 3,500,000L fi While it w'ould be possibleft'o select; from thesee -suitahle number of pe'rn'ruF teams-which would approximately answer 1 thieurequirement for ruidoni distributiom an y' switeh'ing" stagei However; if} at multiplelbe' buii ltu-p from smaller truh k grou ps and each-I selector be caused tochoose'be twecnixon-ly a f'portion -of the trunks; we ar- Referring now to the drawi gs, e lurel ity of incoming?- lines are; sho'Wn warmer-1 iii-inati iigei h ia switch? These svvitelres are d into si'xsi gYO'HpS IitoV Iyeaeh di vide" co riiprisirig" 20 subgroups 0i =five switches each; or one hundred switches; svfitches' -'1 and, 2: represent two; of -a""jg'rou p offi ve' switches each? havilig te'n terminals; Eac h switch? -may be .cor-1s i'dered 5 to represent one 1; v 96 5 audit)? are" four ef aqg oup of switcheg namely, group-I. "Switches Fahd switches, and switches 96" .emd' 97 represent the last-"or 20th sub group: The first'tWo' terminals of sswitches' etc, ofthe first I v sub groupi'are connected: in pelell'eh to the first and fourth trunksof' trunk group A;

while fiheiirst'two terminals of switches 96 Y -andn97 fare'c oiinected iriParallel to the first end; second- :truiiks of :thefisame' triunk group :e ancl';the 'remfiiningisubgroups of switches V hawe their first two terminals "connected t'o' different T combinations," of twe -trunks from group Similarly, the first two terminals of the 'sw-iches of group-II are eonnect'ed'to 105 5 terminals; of the" switches; of groups-IV,-

. Y andVI are connect d, respectively, to trutik's --of the{gi ouj)s D,'E ar1'd"F.-

ill

, first choice for the group.

the trunks of group G, which is also true of all the sub-groups of groups I, II and III. The sub-groups of groups IV, V and V1 have their third, fourth and lifth terminals (JOIIHQClZQtltO combinations of three trunks in group H.

The sixth, seventh, eighth and ninth terminals of all the sub-groups are then connected to combinations of tour trunks from group J and the tenth terminals of all switches are connected to trunk K.

.It'is apparent from inspection thatthis is a graded multiple, since there is a group of trunks individual to each of the groups I, II, III, etc., a subsequent group which is common to groups I, II and III and one which is common togroups IV, V and .VI, while a still additional group is common to all of the groups. I

.The switches 'groups I, II,,III or the groups IV,'V, VI

can hunt over a group of second choice trunks in a difierent, order, and again the random condition is fulfilled. Similarly, the possible permutations of five things taken tour ata time are .120, and the 120 subgroups of switches comprising groups I to VI inclusive, have a perfectly random'access to their third choice trunks. Since the tenth trunk is selected last by each of the switches,

the selection of this trunk is obviously on'a straight,multipling basis. Thus, the multiple illustrated provides a truly random selection within each of the various choices or graded subdivisions.v

i'lhis'm'ultiple represents one possible embodiment of the invention, it being obvious that other arrangen'ients would carry out the spirit of. the invention where the premises, such; as size of switching unit,etc., differ from those assumed in the present illustration. I I

lVhat is claimed is 1; A trunking system in which a plurality of trunks gives service to a plurality of lines. the lines being divided into groups each having access to a number of trunks less than the total number provided, the trunks being divided into a plurality of groups, certain of said groups-0t trunks being assigned as. first choice: trunks to certain of. said as hereinb'efore stated, are divided intosix groups of 100 each,wh1ch groups of lines, certain other of said groups of trunks being assigned as second choice trunks to certain pluralities of said groups of lines and another group of trunkscbeing assigned as third choice trunks in common to all oi said groups'ot lines, the'numbers of theztrunks of each group assigned-to any group o'l 'lines and vthe order in which the trunksare selected being such that when a given number of the total number of trunks are busy the probabilityv oi; one-set of trunks of a given number. being busy will be at least appoximately the same as the prob V ability that any other set of equal number will be busy. 2. A trunking the lines being divided into groups each having access to a'number 0t trunks lesstha-nthev total number provided, the trunks being divided into a plurality of groups, certain of said groups of trunks being assigned as first I so systein'in which a plurality of trunks gives service to a plurality of lines,

choice trunks respectively to certain of said groups of lines, certain other ot said groups of trunks being assigned asvsecon'd choice trunks to certain pluralities of said groups oflines and other groups of trunksbeing assigned as third choice'trunks in common to allot said groups of l nes, thetrunks ot the several groups ottrunks so assigned being interchanged within their respective groups so that the groups of lines having access thereto overlap each other and the order of the selection of the trunks in the various groups of lines and the overlapping otthe groups of lines being-such that when a given number of the total number "oftrunlrs are busy the busy trunks are. at least approxi mately as likely to be one setr of trunks of the given number as any other set of trunks of. equalnumber;

3. Atrunkingsystem inwhicha plurality of trunks :gives service to a plurality of each having access to a number of trunks less than the totalnumber provided. the trunks being divided intoa plurality of groups, certain of said groups of trunks being assigned as first choice trunks respectively to certain of said groups of lines, certainother of saidgroups of trunks being assigned as second choice trunks to certain pl uraliti-es of said lines, the lines being divided into groups groups oflines and another group of trunks being assigned as thirdchoice trunks in com- 1 mon to all of said groups otlines, the trunks of the several groups of trunks so assigned being interchanged within their respective groups according to av rangement, g

At. A trunking system in which a. plurality of trunks gives service to a plurality of lines,

perfectly random arthe lines being divided intogroupsand sub groupseaeh having access to a numberoil trunks less thantlie total number provided,

. the trunks being. dividedinto a plurality of groups, certain of said groups of trunks being assigned as first choice trunks respectively to certain of said groups of lines, certain other of said groups of trunks being assigned as second choice trunks' to certain pluralities of said groups of lines and. other groups of trunks being assigned as third choice trunks in common to all of said groups of lines, the trunks of the several groups of trunkseso assigned being so arranged that each sub-group of lines has access to -a-diflere1it permutation of said trunks.

5. A' trunking system in which a; plurality of trunks gives service-to avplurality', of lines, the lines being divided into groups and sub-groups each having access to a number of trunks less than the total number provided, the trunks being dlvided into a plurality of groups, certain of said groups of trunks being assigned as first cholce trunks,

respectively to certain of said groups of lines, certain other of said-groups of trunks being assigned as SBCOIIClVOhOICB trunks to certain pluralit-ies of said groups of lines and other groups of trunks being assigned as third choice trunks in common to all of said groups of lines, the trunks of the several groups of trunks so assigned being so 'arranged that each subgroup of lines has access to less than the total number of trunks in each of the groups assigned thereto.

' 6. A trunking system in which a plurality oftrunks gives service to a plurality of lines,

the lines being divided into groups and subgroups each having access to a number of trunks less than the total number provided.

vthe trunks being divided into a plurality ofgroups, certain of said groups oftrunks being assigned as first choice trunks respectively to certain of said groups of lines, certain otherof said groups of trunks being asgroups of trunks being assigned as third signed as second choice trunks to certain j pluralities of said groups of lines, and other choice trunks in common to all of said groups permutation of the trunks of each group is used. In testimony whereofi-I have signed my name to'this specification this 25th day of April, 1927. 1 i

' WILLIAMG. BLAUVELT. 

